"It's just whatever's playing in my head," he described. "Like, if you say something, like a trigger word, that could make me sing a song. Like, the guy just came in and said we met in Vienna, and I was like... I started singing 'Don't Cry for Me Argentina.'"

"Which was just weird," Fassbender's Snowman co-star, Rebecca Ferguson, interjected, admitting that she's gotten "quite good at lip-syncing" by following Fassbender around. "We might [take our show on the road]."

"We'll call it 'Snowman: The Musical,'" Fassbender joked.

The Snowman, the film, however is anything but a joke. Fassbender stars in the thriller as a detective working with a brilliant recruit (Ferguson) as they try to track down an elusive serial killer, after investigating the disappearance of a woman whose scarf is found wrapped around an ominous-looking snowman.

The actors filmed the movie on location during a brutal Norwegian winter -- but luckily for Fassbender, he had something special to keep him warm.